Color video signal magnetic recording-reproducing system having a function of optimum recording current level setting

ABSTRACT

Disclosed is a system and method, applicable to color video magnetic recording and reproducing systems, for determining the optimum recording current for each head of a multi-head assembly to produce optimum picture quality. According to the teachings of the invention the scanning tracks of adjacent heads are made to at least partially overlap by causing the magnetic tape to move at a speed slower than normal. A first head records an FM signal modulated by a color test signal while the adjacent head producing an overlapping scanning track reproduces it. The level of the chroma signal of the reproduced and demodulated color test signal is compared with the test signal to control the level of the recording current.

United States Patent 1 [111 3,732,361 Makara 1 May 8, 1973 541 COLORVIDEO SIGNAL MAGNETIC 3,381,083 4/1968 Jensen et al ..l78/5.4 co

RECORDING-REPRODUCING SYSTEM P E R h d M HAVING A FUNCTION OF OPTIMUM"Mary xammer ar RECORDING CURRENT LEVEL Attorney-Sughrue, Rothwell,Mion, Zmn & Macpeak SETTING 57 ABSTRACT [75 1 Inventor: Satoshi MakaraTokyo Japan Disclosed is a system and method, applicable to color [73]Assignee; Nippon Ekctric Company Limited, video magnetic recording andreproducing systems, for determining the optimum recording current forTokyo, Japan each head of a multi-head assembly to produce op- Flledi1971 timum picture quality. According to the teachings of [211 No:126,862 the invention the scanning tracks of adjacent heads are made toat least partially overlap by causing the magnetic tape to move at aspeed slower than normal. [30] Foreign Application Priority Data A firsthead records an FM signal modulated by a color test signal while theadjacent head producing an Mar. 25, 1970 Japan ..45/25447 pp g Scanningtrack reproduces it. The level of the chroma signal of the reproducedand demodulated [52] US. Cl ..l78/5.4 CD ccdor test Signal is comparedwith the test signal to [51 Int. Cl. control the level of the recordingcurrent [58] Field of Search ..l78/6.6 A,'5.4 CD, l78/5.4 AC; 179/1002 B5 References i d 6 Claims, 4 Drawing Figures UNITED STATES PATENTS7/1970 Trost ..l79/l00.2 B

PATENTED MAY 8 I973 SHEET 2 UF 2 I I r COLOR VIDEO SIGNAL MAGNETICRECORDING- REPRODUCING SYSTEM HAVING A FUNCTION OF OPTIMUM RECORDINGCURRENT LEVEL SETTING This invention relates to a magneticrecordingreproducing system having a function of setting an optimumrecording-current, and particularly to such system as four-head typecolor television signal tape recorder in which the tape is scanned by afour-head rotary head assembly in a direction vertical to the runningdirection of the tape.

In four-head type television tape recorders, a carrier signal isfrequency-modulated by a video signal and the frequency-modulated videosignal (FM video signal) is supplied to the rotary head assembly and isdirectly recorded on the tape without a bias signal being supplied bysaturating heads. In such recorders, the high quality picture isobtained when the reproduced RF signal is in the highest level.Therefore, the level of the optimum recording current is alwayscontrolled to provide the maximum reproduced RF signal level.

It is known that the reproduced FM signal level is first increased withthe increase in the recording current to reach a saturation. or amaximum level extending over a fairly broad rangeof the recordingcurrent, and then is decreased. This is in clear contrast to the changein the chroma signal level, which is increased monotonously with theincrease in the recording current.

' sembly having a plurality of heads is rotated at a regular speed; amagnetic tape is transported at a speed lower than a regular tape speed;FM color test signal is recorded by any one of the heads; and therecorded signal is reproduced by the head immediately following said oneof the heads and demodulated; whereby the Generally, the optimumrecording current levels of the heads are different from one another andare changed with abrasion of the heads. Therefore, it is necessary toreset the optimum recording current at regular intervals. 1

Furthermore, in the recording and reproducing of a color video signalhaving a color subcarrier signal (or a chroma signal), the recordingcurrent must be set at a certain value so that the chroma signalsextracted by demodulation from the FM signals reproduced by therespective heads may be maintained at the same level to assure the highquality color picutre.

It has been the practice for setting the optimum recording current thata signal of a certain reference frequency signal (for example, of thecenter frequency of the frequency-modulated video signal) is recorded onthe magnetic tape at various recording current levels. In reproduction,the recorded referencefrequency signal is reproduced and measured atevery recording current levels. The results are plotted to make arecording-reproducing characteristic curve (electromagneticcharacteristic). From this curve, the optimum recording current level iscalculated. In a monochrome television video tape recorder, this maximumreproduced RF signal level corresponds directly to the optimum recordingcurrent level.

In a color television video tape recorder, however, an RF signalmodulated by a color test signal such as a color bar signal is recordedon the tape at the optimum recording current level determined in theabove-mentioned manner. Then, the recording tracks are scanned in turnby any one of the four heads to reproduce RF signals, which are thendemodulated to chroma signals. The chroma signals corresponding to therespective heads are compared in their levels with one another. If anydifferences are detected between these levels, the recording currentlevels are finely adjusted to get rid of such differences.

recording current level is manually adjusted by observing the reproducedsignal level or the reproduced picture.

In a four-head standard television video tape recorder, four heads aredisposed at intervals of on a circumference of a head drum having adiameter of 2 inches. The head drum is rotated at a speed of 240revolutions 'per second. A 2-inch wide magnetic tape is transported at aspeed of 15 inches per second. This tape is partly curved like an arc bya female guide at the head drum portion. This brings the tape into firmcontact with the drum circumference, whose length corresponds to itscentral angle of about Thus, the tape is scanned by the magnetic head atthe relative speed of 1,500 inches/sec. in the direction nearlyperpendicular to the transport direction. The four heads have the samestructure.

In recording, the same FM signal is supplied to these headssimultaneously. The width of each head is 10 mils and accordingly thewidth of the video recorded tracks are 10 mils. The recorded tracks arealigned on the tape at intervals of 5 mils, slightly slanted at anglesof about 33 minutes with respect to the lateral direction ofthe tape asshown in FIG. 1. (A).

Assuming that the drum is rotated at the normal speed, and the tapespeed is slowed down to less than half, the pitch of the recording trackis reduced to less than half. As a result, an overlapped area is formedamong the recorded tracks of the mutually adjacent 5 magnetic heads.Under this condition, one of the heads serves as a recording head andanother one which immediately follows the mentioned one serves as areproducing head. Then, the signal recorded on the overlapped area isreproduced by another following head, and the recording current of thesignal applied to the recording head can be adjusted by observing thereproduced signal picked up by the following head so as to obtain thehighest quality picture.

Furthermore, if a signal modulated by the color test signal is appliedto the recording head, the recording current of the color televisionsignal can be also adjusted.

Now the features and advantages of the invention will be clearlyunderstood from the following detailed description of a preferredembodiment of the invention taken in connection with the accompanyingdrawings, wherein:

FIG. 1 shows positional relationship on a tape between recorded tracksand reproducing area;

FIG. 2 is a block diagram of an embodiment of the invention; 1

FIG. 3 is a waveform diagram for signals appearing at various parts ofthe embodiment shown in FIG. 1; and

FIG. 4 shows relationship of the reproduced chroma signals.

Referring to FIG. 1, FIG. 1(B) shows the relationship between therecorded track (as indicated by the full line) of one of the recordingheads and the tape scanning track (as indicated by the dotted line) ofthe another head immediately following the mentioned one, under thecondition of the normal tape transport speed. FIG. 1(C) shows therelationship between the recording track and the tape scanning trackwhen the tape speed is half of the normal speed. In this case, the

' width of the overlapped area between the recording track and thescanning track of the following head is about 2.5 mils. While, FIG. 1(D)shows the positional relationship between the recording track and thetape scanning track, observed under the condition where the tape speedis about one-third of the normal speed. In this case, the width of theoverlapped area is about 5 mils. In other words, the lower the tapespeed is, the wider the overlapped area will be.

The signals modulated by color test signal are reproduced in sequence bythe immediately following head with respect to each of the four heads,and the recording current level adjusting means provided for each of theheads is set to make the level of the reproduced chroma signal iscoincident with the nonrecorded reference chroma signal level. Thus, theoptimum recording current value can be set.

According to this method, reproduction by the immediately following headis achieved almost simultaneously with recording. Therefore, therecording current adjusting means can be continuously controlled in theabove-mentioned manner, so that the reproduced chroma level may becoincident with the non-recorded chroma level, without requiringrepetition of recording and reproduction. Thus, the optimum recordingcurrent level can easily be set in a short period of time.

Referring to FIG. 2, a relay control voltage is applied to terminals 32and 33. When head selection switches 34 and 34 are placed to contacts 35and 35 respectively, a relay 3 is actuated, and first magnetic head isconnected to a recording amplifier 7 by way of a make-contact 3' of therelay 3. The magnetic head assembly 100 comprises magnetic heads 101,102, 103 and 104, which are disposed on the drum circumference. The tapeis scanned in sequence by the magnetic heads 10], 102, 103 and 104.

A color test signal applied to the tenninal 29 is frequency-modulated bya modulator l6 and the modulated signal is applied to a recording gatecircuit and a reproducing gate circuit 22. When the recording gatecircuit 15 is opened by a tachometer pulse (as will be described later)during the scanning of a tape (not shown) by the first magnetic head101, the FM signal supplied from the modulator 16 is passed through therecording gate circuit 15 and is level-controlled by a recording currentadjuster and then amplified by a recording amplifier 7. The amplifiedsignal is recorded on the tape by the first magnetic head 101. Thesignal from the gate circuit 22 is demodulated to a video signal by ademodulator 23. The chroma component is derived by a high-pass filter 24and used as a chroma reference signal to be delivered from a terminal31.

During the scanning of the tape by the second magnetic head 102 afterthe first magnetic head 101 has completed recording the signal on thetape, the

reproducing gate circuit 22 operates to, block the FM plied to areproducing amplifier 12 through a break I contact 4' of a relay 4. Thereproduced signal from the reproducing amplifier 12 is supplied to thedemodulator 23 through a reproducing equalizer 202 and reproducing gatecircuit 22, and demodulated to a video signal. This video signal issupplied to the highpass filter 24, whose output is delivered from theterminal 31 as the reproduced chroma signal. The reproducing equalizergroup 200, comprising reproducing equalizers 201, 202, 203 and 204 ofidentical characteristics, is adjusted so that correct chroma level canbe demodulated when the signal recorded at the correct recording currentlevel is reproduced from the tape.

A rotating phase detector such as tachometer (not shown) is directlyconnected to the head drum on which the heads are installed. Thus thedrum rotating phase is detected in the form of symmetrical square waveof repetition period T as shown in FIG. 3(A). This square wave pulse istachometer pulse which is applied to a delay circuit 18 through aterminal 30 in FIG. 2. The pulse delay circuit 18 is, for example, amonostable multivibrator circuit, in which a pulse delay time can bechanged by switching a time constant circuit. When the switch 34' isconnected to the terminal 35', the delay time of the pulse delay circuit18 is set to 1 (FIG. 3) by the delay time adjusting means 39 whichdetermines the rise time of the recording gate pulse (FIG. 3B). Thisrise time is the time at which the magnetic head to be set the optimumrecording current starts scanning the tape. The recording gate pulse isprovided from a circuit such as the monostable multivibrator 19. Thisgate pulse drives the recording gate 15 by way of a drive circuit 17.The width of the recording gate pulse is set to T/4 by an adjustingmeans 43.

The reproducing gate pulse (FIG. 3C) is provided from a circuit such asa monostable multivibrator 20. The monostable multivibrator 20 istriggered by the trailing edge of the recording gate pulse, and thewidth of the reproducing gate pulse is set to T/ 4 by another Iadjusting means 44. This reproducing gate pulse drives the reproducinggate circuit 22.

When the head selection switches 34 and 34 are connected to terminals 36and 36 respectively, a relay 5 is actuated and the magnetic head 103 isconnected to a recording amplifier 9. And a recording gate pulse asshown in FIG. 3(D) and a reproducing gate pulse as shown in FIG. 3(E)are obtained by the circuits l9 and 20, respectively. The delay time ofthe delay circuit 18 is adjusted to t (FIG. 3) by a delay adjustingmeans 40. The FM signal from the modulator 16 is caused to pass throughthe recording gate circuit 15, a level adjuster 27, recording amplifier9, and the make-contact 5' of the relay 5 and then recorded on the tapeby the third magnetic head 103. The recorded signal is reproduced by thefollowing fourth magnetic head 104 and applied to the reproducing gatecircuit 22 through a break-contact 6 of a relay 6, a reproducingamplifier 14, and a reproducing equalizer 204. The signal is then gatedby the reproducing gate circuit 22. demodulated to a video signal by thedemodulator 23. The video signal is then caused to pass through thehigh-pass filter 24, and delivered as a reproducing chroma monitorsignal from the terminal 31.

Similarly, when the head selection switches 34 and 34 are connected toterminals 37 and 37' respectively, the relay 6 is actuated. The FMsignal passing through the recording gate circuit by the recording gatepulse as shown in FIG. 3(F) is recorded by thefourth magnetic head 104.The recorded signal is reproduced by the first magnetic head 101, andapplied to the reproducing gate circuit 22, and delivered as a monitoroutput of the fourth magnetic head 104. In this operation, the delaytime of the delay circuit 18 is set to T, as shown in FIG. 3(G).

When the head selection switches 34 and 34' are connected to theterminals 38 and 38' respectively, the relay 4 is acturated. The FMsignal caused to pass through the recording gate circuit 15 by arecording gate pulse as shown in FIG. 3(H) is recorded by the secondmagnetic head 102. The recorded signal is reproduced by the thirdmagnetic head 103 and applied to the demodulator 23 through the gate 22by the reproducing gate pulse as shown in FIG. 3(J)-, and delivered as amonitor output of the second magnetic head I02. I

In FIG. 4, the portions 1 and 1' denote reference chroma signal levelsof FM signal extracted from the modulator 16, and the portions 301, 302and 303 represent reproduced chroma signal levels. FIG. 4(A) shows thatthe reproduced chroma signal level is coincident with the referencechroma signal level. In other words, FIG. 4(A) shows the state where therecording current setting is completed. FIGS. 4(8) and 4(C) show thatthe recording current level are low and high respectively.

Thus, according to this invention, the optimum recording current levelcan be easily set in a short period time, while the reproduced signal isbeing observed during the recording operation. Furthermore, since therecording current can be varied continuously by virtue of simultaneousreproduction feature, it is possible to exactly set the optimum currentlevel.

What is claimed is:

1. In a color video magnetic recording and reproducing system includinga head assembly having a plurality of heads, each head having associatedtherewith a recording and a reproducing amplifier means, the

recording amplifier means including recording current level controlmeans, the head assembly rotating to cause each of the plurality ofheads to scan a moving magnetic tape to produce a plurality of scanningtracks, one corresponding to each registration of a head with the tape,the improvement comprising:

a. means for controlling the tape speed to cause the scanning tracks ofadjacent heads to at least partially overlap,

b. means for frequency-modulating a carrier wave in response to a colortest signal including a chroma component,

c. means for applying the frequency-modulated (FM) signal to one of theheads and thence to the tape through the recording amplifier associatedwith said one of the heads,

d. means for causing the adjacent head producing a scanning track atleast partially overlapping the recorded track to reproduce the recordedsignal,

e. means for demodulating the reproduced recorded signal to provide thechroma component included in the demodulated color test signal forcomparison with the level of the chroma component included in saidrecording color test signal, and

f. means for controlling the recording current level control means toachieve an optimum recording current level.

2. The color video magnetic recording and reproducing system of claim 1wherein said means for applying the FM signal includes recording gatemeans and said means for reproducing said recorded signal includesreproducing gate means, said improvement further comprising timing meanscoupled to said recording and reproducing gate means and responsive tothe rotation of said head assembly for controlling the switching of saidgate means.

3. The color magnetic recording and reproducing system of claim 2wherein said timing means comprises:

a. means responsive to the rotation of said head assembly for generatinga reference signal,

b. first pulse producing means for enabling said recording gate to passsaid applied signal over a first predetermined time interval,

c. delay means for delaying said reference signal so that said delayedreference signal energizes said first pulse producing means when saidone of the heads begins scanning the magnetic tape,

d. second pulse producing means, responsive to the first pulse means,for enabling said reproducing gate to pass said reproduced signal over asecond predetermined time interval, and

e. output means coupled to said reproducing gate means for providingsaid signal at an output for comparison with said level of chromacomponent included in said recording color test signal.

4. The color video magnetic recording and reproducing system of claim 3further including switch means for selectively electrically connectingeach of the plurality of heads, one at a time, to its associatedrecording amplifier, and'means for controlling the delay time introducedby said delay means to assure activation of said recording gate meansupon the initiation of a sanning track by a head electrically connectedto its corresponding recording amplifier.

5. The color video magnetic recording and'reproducing system of claim 1wherein said means for con-' trolling the recording current level iscaused to control said recording current level so that the level of saidreproduced chroma component may be coincident with the level of thechroma component included in said recording color test signal.

6. In a video magnetic recording and reproducing system including a headassembly having a plurality of heads, each head having associatedtherewith a recording and a reproducing amplifier means, the recordingamplifier means including recording current level control means, thehead assembly rotating to cause each of the plurality of heads to scan amoving magnetic tape to produce a plurality of scanning tracks, onecorresponding to each registration of a head with the tape, a method fordetermining optimum recording current levels to each of said headscomprising the steps of:

causing the speed of the said magnetic tape relative to said headassembly to be sufficiently slow to cause at least partial overlappingof scanning tracks produced by adjacent heads,

frequency modulating a carrier wave in response to a color test signalincluding a chroma component,

applying the frequency modulated signal to one of -the heads and thenceto the tape through the recording amplifier means associated with saidone 10 of the heads,

causing the adjacent head producing a scanning

1. In a color video magnetic recording and reproducing system includinga head assembly having a plurality of heads, each head having associatedtherewith a recording and a reproducing amplifier means, the recordingamplifier means including recording current level control means, thehead assembly rotating to cause each of the plurality of heads to scan amoving magnetic tape to produce a plurality of scanning tracks, onecorresponding to each registration of a head with the tape, theimprovement comprising: a. means for controlling the tape speed to causethe scanning tracks of adjacent heads to at least partially overlap, b.means for frequency-modulating a carrier wave in response to a colortest signal including a chroma component, c. means for applying thefrequency-modulated (FM) signal to one of the heads and thence to thetape through the recording amplifier associated with said one of theheads, d. means for causing the adjacent head producing a scanning trackat least partially overlapping the recorded track to reproduce therecorded signal, e. means for demodulating the reproduced recordedsignal to provide the chroma component included in the demodulated colortest signal for comparison with the level of the chroma componentincluded in said recording color test signal, and f. means forcontrolling the recording current level control means to achieve anoptimum recording current level.
 2. The color video magnetic recordingand reproducing system of claim 1 wherein said means for applying the FMsignal includes recording gate means and said means for reproducing saidrecorded signal includes reproducing gate means, said improvementfurther comprising timing means coupled to said recording andreproducing gate means and responsive to the rotation of said headassembly for controlling the switching of said gate means.
 3. The colormagnetic recording and reproducing system of claim 2 wherein said timingmeans comprises: a. means responsive to the rotation of said headassembly for generating a reference signal, b. first pulse producingmeans for enabling said recording gate to pass said applied signal overa first predetermined time interval, c. delay means for delaying saidreference signal so that said delayed reference signal energizes saidfirst pulse producing means when said one of the heads begins scanningthe magnetic tape, d. second pulse producing means, responsive to thefirst pulse means, for enabling said reproducing gate to pass saidreproduced signal over a second predetermined time interval, and e.output means coupled to said reproducing gate means for providing saidsignal at an output for comparison with said level of chroma componentincluded in said recording color test signal.
 4. The color videomagnetic recording and reproducing system of claim 3 further includingswitch means foR selectively electrically connecting each of theplurality of heads, one at a time, to its associated recordingamplifier, and means for controlling the delay time introduced by saiddelay means to assure activation of said recording gate means upon theinitiation of a scanning track by a head electrically connected to itscorresponding recording amplifier.
 5. The color video magnetic recordingand reproducing system of claim 1 wherein said means for controlling therecording current level is caused to control said recording currentlevel so that the level of said reproduced chroma component may becoincident with the level of the chroma component included in saidrecording color test signal.
 6. In a video magnetic recording andreproducing system including a head assembly having a plurality ofheads, each head having associated therewith a recording and areproducing amplifier means, the recording amplifier means includingrecording current level control means, the head assembly rotating tocause each of the plurality of heads to scan a moving magnetic tape toproduce a plurality of scanning tracks, one corresponding to eachregistration of a head with the tape, a method for determining optimumrecording current levels to each of said heads comprising the steps of:causing the speed of the said magnetic tape relative to said headassembly to be sufficiently slow to cause at least partial overlappingof scanning tracks produced by adjacent heads, frequency modulating acarrier wave in response to a color test signal including a chromacomponent, applying the frequency modulated signal to one of the headsand thence to the tape through the recording amplifier means associatedwith said one of the heads, causing the adjacent head producing ascanning track at least partially overlapping the recorded track toreproduce the recorded signal, demodulating the reproduced recordedsignal to provide the chroma component included in the demodulated colortest signal, and comparing the level of the reproduced chroma componentwith the level of the chroma component included in said recording colortest signal.